1. Field of the Invention
The invention relates to a proximity exposure device with a distance adjustment device for setting the distance between a mask and a workpiece.
2. Description of Related Art
In proximity printing, a mask and a workpiece are fixed adjacent to one another, essentially parallel light is emitted from the mask side onto the workpiece, between the mask and the workpiece a microscopically small intermediate space being formed, and thus, the mask pattern is transferred onto the workpiece.
The reason that a microscopically small intermediate space is formed between the workpiece and mask is to avoid various types of damage, such as scratches on the mask or the workpiece by contact of the mask with the workpiece, mask impurities due to adhesion of a photo-resist film and the like formed on the workpiece on the mask, and similar damage.
To adjust the microscopically small intermediate space between the mask and workpiece, a process is conventionally used in which a strip, a sphere, and the like of metal or resin is inserted between the mask and workpiece as a spacer. In this process, the desired distance can be easily adjusted if the thickness of the spacer is selected (measured) beforehand.
This process prevents the mask and workpiece from coming into contact with one another over their entire surface. Therefore, the above described damage to which the mask and workpiece are subject can be reduced. Since, however as before, the mask and workpiece are partially in contact with one another via the spacer, the above described damage cannot be completely prevented.
To eliminate the above described defect, for example. Japanese patent disclosure document HEI 3-38024 and Japanese patent disclosure document HEI 3-38025 suggested measures. In the technology described in these two publications, there is a means for distance measurement and the described distance is set without contact of the mask with the workpiece. In this case, at three points within the mask surface/workpiece surface the distance is measured, the tilt of the workpiece carrier is adjusted such that the distances at the three points become the desired distances, and thus, the desired distance is reached without contact.
In the process described in the two aforementioned publications for distance measurement, in an optical system for measurement purposes, there is a mask on which a strip-like pattern is formed which is projected on the workpiece and mask, projected images being observed. Based on the difference between the position at which the projection image is focused on the mask, and the position at which the projection image is focused on the workpiece, the size of the distance is measured.
Furthermore, distance measurement processes for the same purpose are known from Japanese patent disclosure document SHO-63-138730, Japanese patent disclosure document HEI 5-226215, Japanese patent disclosure document HEI 6-5486, and Japanese patent disclosure document HEI 6-283400 and the like.
In the technology described in Japanese patent disclosure document SHO 63-138730, using an axicon, a halo (light ring) is formed which is emitted onto a mask and a workpiece, reflected light being picked up by a photo detector of the double ring type. Due to the different lengths of the optical path, as a result of the distance between the mask and the workpiece, the size of the halo reflected by the mask differs from the size of the halo reflected by the workpiece. This difference is determined by the photo detector of the double ring type, by which the value of the distance is measured.
In the technology described in Japanese patent disclosure document HEI 5-226215, there are beam-optical components, such as a diffraction grating, a zone plate, a grating lens and the like at locations on the mask where a measurement is desired. A light flux is obliquely incident through the aforementioned components in the workpiece and is reflected. The location of the spot of reflected light which has passed again through the beam-optical components and which has an angle of reflection which has been changed, is measured by means of a line sensor, by which the value of the distance is measured.
In the technology described in Japanese patent disclosure document HEI 6-5486, light from the bottom of the workpiece is obliquely incident. In a light receiving part which is likewise located on the bottom of the workpiece, the amount of deviation of the position of the light reflected from the mask surface from the position of the light reflected by the workpiece surface is determined, by which the amount of distance is measured.
In the technology described in Japanese patent disclosure document HEI 6-283400, a parallel light flux from the side of the mask and the workpiece is obliquely incident on the sides of the mask/workpiece. Either the intensity of the light which is broken by the mask/workpiece and has passed through, or the intensity of the light which has passed through the intermediate space, is measured. Here, the size of the distance is measured by using the relationship between the light intensity and the size of the distance.
In the above described prior art, the disadvantages are as follows:
(1) In the technology described in Japanese patent disclosure document HEI 6-38024, at measurement points of the mask and workpiece, reflection films are formed which reflect light to obtain reflected light intensity sufficient for observation of projected images. PA1 Since here the measurable locations are limited to those where reflection films are formed, a measurement cannot be taken just anywhere on the mask/workpiece. The measurement areas are provided with reflection films which are unnecessary for a component, for example, of a liquid crystal display device or the like which is to be produced. Therefore, it is necessary to safeguard an area on the workpiece for measurement except for the area in which the component is formed. As a result, there is the disadvantage of a poor degree of utilization of the workpiece material. Furthermore, there is the disadvantage of an increase of production costs because, in the case of later removal of the reflection films, a process for removal of the reflection films is added to the production process. PA1 (2) In the technology described in Japanese patent disclosure document HEI 3-38025, in which the technology described in Japanese patent disclosure document HEI 3-38024 is improved, reflection films are unnecessary. As follows from the publication, in the case of a small distance between the mask and workpiece a clear, strip-like pattern cannot be obtained because the intensity of the light reflected by the mask is essentially the same as the intensity of the light reflected by the workpiece and interference occurs. PA1 Therefore, first of all, when the distance between the mask and workpiece at which no interference occurs is sufficient, a measurement is taken. Afterwards, the distance is reduced until a distance for actual exposure is reached and the exposure is performed. Therefore, it cannot be directly confirmed whether the distance at which, in fact, exposure is performed has the desired value. PA1 The accuracy of the distance adjustment during exposure is determined by the accuracy of the movement device which sets the distance during measurement to the exposure distance. Therefore, there is the disadvantage that movement errors can neither be confirmed nor corrected, even if they are present. PA1 (3) In the technology described in Japanese patent disclosure document SHO 63-138730, the disadvantage is the same as in Japanese patent disclosure document HEI 3-38025 because, in the case of a small distance, the intensity of the light reflected by the mask is essentially the same as the intensity of the light reflected by the workpiece, interference occurs, and a clear halo cannot be obtained. PA1 (4) In the technology described in Japanese patent disclosure document HEI 5-226215, it is necessary to locate beam-optical components, such as a diffraction grating, a zone plate, a grating lens and the like, at the locations on the mask where measurement is desired. Therefore, there are the disadvantages that a measurement cannot be taken just anywhere and the mask is costly. PA1 (5) In the technology described in Japanese patent disclosure document HEI 6-5486, it is necessary to insert the light source for purposes of measurement and the light detection part underneath the workpiece, i.e., within the workpiece carrier, which holds the workpiece stationary. For this reason, the arrangement of the workpiece carrier is extremely limited. Furthermore, there is the disadvantage that a measurement outside of the location where it is inserted cannot be taken, and therefore, measurement just anywhere is not possible. PA1 (6) In the technology described in Japanese patent disclosure document HEI 6-283400, based on the feature of the measurement process in a measurement of the center areas of the mask/workpiece, the light intensity information is obtained as a result of the distance between the center areas together with the light intensity information based on the distance between the outside peripheral areas. Therefore, there is the disadvantage that the distance between the center areas cannot be exactly measured. This disadvantage becomes more pronounced, the larger the mask/workpiece. As a result, this technology cannot be used, especially in the case of treatment of a large mask/large workpiece as in the production of a video display element, such as a liquid crystal display device element and the like. PA1 (1) In a proximity exposure device which has an ultraviolet irradiation part for irradiation with UV radiation, a mask carrier part for holding the mask stationary, a workpiece carrier part for holding a workpiece stationary in a state in which the workpiece is adjacent to but at a distance from the mask, and a distance calibration device which is connected to the workpiece carrier and adjusts the distance between the workpiece and the mask, there are a distance measurement part, a device for moving the distance measurement part which continuously or incrementally moves the distance measurement part in a direction perpendicular to the mask and workpiece, a position detector for determining the position of the distance measurement part, and an arithmetic and logic unit for computing the distance between the mask and workpiece, in the distance measurement part there being a light source for measurement purposes, a beam splitter, a pinhole plate, an objective lens and a light detection device. A light source for measurement purposes is arranged such that the light emitted from this light source is focussed via the beam splitter onto the pinhole plate. The pinhole plate is located at a site which represents the focal point of the objective lens which is opposite the focal point on the object side and where the light from the light source for measurement purposes which has passed through the pinhole plate is focussed on the focal point on the object side of the objective lens. The light detection device is located at a site where the light is detected which has been reflected by the mask and workpiece, and which has passed through the objective lens, at least one pinhole, and the beam splitter. The value of the distance between the mask and workpiece is computed based on the intensity of the output signal from the light detection device and based on the output signal from the position detector by the arithmetic and logic unit. PA1 (2) The objects are furthermore achieved in accordance with the invention by the pinhole of the pinhole plate being formed of a collection of several pinholes, in solution (1). PA1 (3) The objects are furthermore achieved according to the invention by there being a second light detection device in the distance measurement part, in solutions (1) and (2), by the beam splitter being aligned such that the light from the light source for measurement purposes is divided into two parts, one part of which is radiated onto the pinhole plate and the other part of which is incident on the second light detection device, by the output signals from the light detection device and second light detection device being computed in the arithmetic and logic unit, and thus, fluctuation of the light intensity of the light source for measurement purposes is corrected. PA1 (4) The objects are, furthermore, achieved in accordance with the invention by a polarizing beam splitter being used as the beam splitter, in solutions (1), (2) and (3), by the light emitted from the light source for measurement purposes being polarized in the first polarization direction by this polarizing beam splitter, and at the same time, this light with the first polarization direction being passed, by light with the second polarization direction which differs from the first polarization direction being incident on the light detection device, and furthermore, by a quarter wave plate being located in the optical path between the pinhole plate and the focal point on the object side, by which quarter wave plate the light polarized by the polarizing beam splitter with the first polarization direction is converted into a circular polarization, and at the same time, the light reflected by the mask and workpiece with the circular polarization is converted into light with the second polarization direction. PA1 (5) The objects are, furthermore, achieved according to the invention by there being a second light source and image detection element in the distance measurement part, in solutions (1), (2), (3) and (4), by the second light source being located at a site where the light emitted from this light source is irradiated through the objective lens onto the mask and workpiece, and by the image detection element being located at a site where the images of the mask and workpiece are detected. PA1 (6) The objects are furthermore achieved in accordance with the invention by a mask being used for purposes of production of an image display element, in solutions (1), (2), (3), (4), and (5), and by the cross sectional shape of the light flux from the light source for measurement purposes being formed on a surface on which the mask pattern of a shape which can be encompassed by an opening formed in the mask pattern area. PA1 (7) In addition to a proximity exposure device, the invention also relates to a process for determining the distance between the mask and a workpiece.